This research proposal is aimed at developing a useful host-mediated assay system for screening potential mutagenic and carcinogenic agents, using human hemopoietic cell lines as a test system. The methods consist of growing human cells in diffusion chambers, implanting them in the peritonial cavities of mice injected with the test chemicals, and allowing these cells to proliferate for a few days. These cells would then be taken out and cultured in RPMI 1640 medium, and analyzed for chromosome damage as well as their transformability using SV 40 virus. An in vitro study to find the dose effect curves of these cells, using the pesticides, would also be initiated. The criteria for transformability would be: (1) chromosome constitution study, (2) cell cycle time study, and (3) colony formation study, using agar plate technique. Correlations of mutagenicity and transformability would hopefully be obtained, which would reinforce the hypothesis that the primary carcinogenic action involves a mutagenic event, brought about by environmental mutagens, such as pesticides.